Cucurbits Diseases, Symptoms, Etiology, Disease cycle and Their Management. 1)Downy mildew 2)Powdery mildew 3)wilt 4)Angular leaf spot 5)Mosaic 6)TOSPO virus

1. Cucurbits Diseases, Symptoms, Etiology,
Disease cycle and Their Management.
1. Downy mildew
2. Powdery mildew
3. wilt
4. Angular leaf
spot
5. Mosaic
6. TOSPO virus
: Pseudoperonospora cubensis
: Erysiphe
cichoracearum,
Sphaerotheca fuligena
: Fusarium oxysporum f.sp. niveum
: Pseudomonas syringae pv.
lachrymans
:Cucumber mosaic virus
: Tomato spotted wilt virus
(TSWV)

2. 1. Downy mildew : Pseudoperonospora cubensis
Host Members of Cucurbitaceae, the gourd family, including
cucumber (Cucumis sativus), squash (Cucurbita spp.), melon
(Cucumis melo) and watermelon (Citrullus lanatus).
 Symptoms:
Cucumber, squash and pumpkin
Downy mildew symptoms first appear as small yellow spots or water-
soaked lesions on the topside of older leaves.
 The centre of the lesion eventually turns tan or brown and dies.
 The yellow spots sometimes take on a "greasy" appearance and do not
have a distinct border.
During prolonged wet periods, the disease may move onto the upper crop
canopy.
This is the earliest symptom produced by the disease, but will disappear as
moisture dissipates.
Early lesions are light green in appearance and become chlorotic and
finally necrotic as host plant cells die.
Severe infection results in leaves that are completely dead and curled up.
This symptom has been described as “wildfire” as the leaves appear to be
burned.
A greater proportion of mishapen fruit (especially incucumber)

3. Watermelon and cantaloupe.
Symptoms on watermelon and cantaloupe are typically irregular shaped
lesions on the foliage that turn brown rapidly.
Infected leaves may experience an upward leaf curl
In cantaloupe crops, the lesions appear irregular shaped, whereas the
lesions are smaller and rounder on infected watermelon leaves.
As the disease progresses, the lesions expand and multiply, causing the
field to take on a brown and "crispy" appearance.

4. Etiology:
P. cubensis is an obligate parasite . The mycelium is coenocytic
and intracellular with small finger like haustoria. 1-5 sporangiophores
arise through stomata. Spore bearing tip are subacute. Sporangia are
grayish to olivaceous purple. Ovoid to ellipsoidal, thin walled with
distal papilla & 21-39 µm X 14-23µm. Zoospore are 10-30µm in dia.
Oospore are not common.
Disease cycle :
P.I: Collateral hosts or fungus surviving in plant debris
S.I:Wind borne sporangia or splashing rain water
Management
 Destruction of cucurbitaceous weeds around field
Avoid excess overhead irrigation.
Wider spacing and planting sites with good drainage.
Seed treatment with Apron at 2 g/kg.
Spray metalaxyl@0.2% or chlorothalonil@0.2%
 Spray zineb@0.3% at 10 days interval

5. 2. Powdery mildew : Erysiphe cichoracearum or Sphaerotheca
fuligena
 Symptoms :
Powdery mildew forms obvious patches of whitish mycelium
(resembling talc) on upper and lower leaf surfaces, petioles, and
stems.
First noted on the older leaves, powdery mildew appears as pale
yellow spots on stems, petioles, and leaves.
These spots enlarge as the white, fluffy mycelium grows over plant
surfaces and produces spores, which give the lesions a powdery
appearance.
Affected leaves become dull, chlorotic, and may show some degree
of wilting in the afternoon heat; eventually they become brown and
papery.
The diseased areas turn brown and dry. This leads to premature
defoliation and death
Fruits remain undeveloped and are deformed

6. Etiology:
E. Cichoracearum the conidia measure 63.8X 31.9 µm. The
clestothecia are globose 80-100 µm in dia., containnig 10-15 asci,
which are 58-90 µm in size.each ascus contains two ascospores and
are oval or sub cylindrical.
S. fulinginea occasionaly brownish when old. Conidia are in
chains with fibrisin bodies, ellipsoid to barrel-shaped and 25-37 X
14-25 µm. Conidial germ tubes mostly forked perithecia areround,
66-98 µm in dia. Asci are broadly elliptic and are 50-80 X 30-60 µm.
In each ascus 8ellipsoid ascospores are found.

7. Disease cycle:
P.I: Collateral hosts or through Cleistothecia
S.I:Wind borne conidia
Management
Plant resistant varieties where available.
Choose planting sites with good air movement and free of shade.
Spray Calixin 0.1% or Karathane @0.2%

8. 3. Wilt : Fusarium oxysporum f.sp.
niveum
 Symptoms:
 Symptoms can occur at any stage of growth
On young seedlings, a hypocotyl rot and damping-off may occur. In
older plants, there is marginal yellowing progressing to a general
yellowing of the older leaves, and wilting of one or more runners.
In some cases, sudden collapse occurs without any yellowing of the
foliage.
On stems near the crown of the plant, a linear, necrotic lesion may
develop, extending up the plant and usually on one side of the vine.
One runner on a plant may wilt and collapse, with the rest of the
runners remaining healthy.
In a wet weather , a white or pinkish fungus growth develops on the
surface of dead stems.
Vascular discoloration should be evident and is very diagnostic.
Mature plants often wilt severely (collapse) late in the season because
of the fruit load stress.

9. Etiology :
The fungus produces three types of spores, small colourless,
oval to narrowly elliptical, non-septate microconidia, lagre sickle
shaped, septate macro-conidia and thick walled Chlamydospores.

10. DISEASE CYCLE OF WILT
The fungus can survive in soil as saprophyte for many years
and chlamydospores act as resting spores. The pathogen is both
externally and internally seed-borne. The primary infection is
mainly from dormant hyphae and chlamydospores in the soil. The
secondary spread is through conidia and chlamydospores which are
disseminated by wind
and irrigation water.
MANAGEMENT
Treat the seeds with Carboxin or Carbendazim at 2 g/kg.
Apply increased doses of potash with a balanced dose of
nitrogenous and phosphatic fertilizers.
organic
Apply heavy doses of farm yard manure or other
manures. Follow mixed cropping with non-host plants.
Use resistant varieties.
 Maintaining a pH of 6.5 to 7.0.

11. 4. Angular leaf spot: Pseudomonas syringae pv.
lachrymans
 Symptoms:
Small, round water-soaked spots appear on leaf tissue, and expand until
they are confined by veins, giving them the characteristic angular look.
Under moist conditions a milky white exudates containing bacterial cells
may ooze out of the lesion on the lower leaf surface.
These wet-looking spots will dry out and turn yellow-brown or the dead
tissue may fall out leaving a “shot-hole” appearance.
Yellowing of the leaf between lesions may occur where disease severity is
high.
Similarly, water-soaked spots may appear on stems and petioles, drying
out to form a whitish crust.
Spots can also appear on fruit, where they are tiny and water-soaked but
dry to form whitish, chalky, spots.
These spots cause internal decay of fruit, and fruit that is infected early
may be deformed. Affected plants will grow poorly, produce less fruit, and
affected fruit is unmarketable.

12. Etiology :
The bacterium is gram negative, aerobic and rod shaped motile with 1-5
polar flagella & 0.8-1.2 µm in length.
It forms capsule and green fluorescent pigment in culture.

13. Disease cycle:
The Pseudomonas bacterium is a seed
borne pathogen. In addition, the
pathogen can overwinter in infested crop residues. The secodary spread
through irrigation water.
Management
Plant certified, pathogen-free seed produced in arid western locations.
Resistant cucumber varieties are available.
Do not grow cucurbits in the same field more than once every three or four
years and avoid excessive nitrogen fertilization.
Limit the use of overhead irrigation and avoid cultivating, harvesting, or
otherwise handling plants when they are wet.
Where ever feasible, cleanly plow under or collect and burn crop debris
immediately after harvest.
Apply a recommended bactericide at first sign of disease.
(Streptocycline/Streptomycine). Spray 400ppm Streptomycin sulphate.
Tank-mix the recommended bactericide with effective fungicides to protect
the plants against fungal diseases.

14. 5. Cucumber Mosaic: Cucumber mosaic
virus
Symptoms
Symptoms of CMV in cucurbits generally manifest as severe stunting,
prominent yellow foliar mosaic, plant and leaf malformation, and stunting
due to drastic reduction of leaf size and stem internodes.
When the virus becomes systemic, leaves prominently curl downward,
develop a mosaic pattern, and remain small.
Flowers develop abnormalities and have greenish petals.
Foliar and flower symptom intensity varies with species and cultivar:
symptoms are most severe in summer squash, some pumpkins, and many
melons and less severe in cucumber, winter squash, and watermelon.
Infected fruit are often distorted and discolored, remain small, and, when
severely infected, produce a negligible amount of seeds.
Survival and spread
 Survive on weeds, ornamentals or other crops
 Transmitted by aphids (Aphis craccivora, Myzus persicae) and spotted
and
striped cucumber beetles
Collateral hosts: Banana, clover, corn, passion fruit, safflower, spinach,
sugarbeet, wild cucumber, Commelina communis, C. diffusa, C. nudiflora,
Solanum elaegnifolium, Phytolacca sp., periwinkle, Gladiolus sp., Impatiens

15. Management
Rogue out infected plants
Eliminate perennial weed hosts
Vector control by spraying monochrotophos or phosphamidon,
1.5 ml per liter of water

16. 3. TOSPO virus : Tomato spotted wilt virus (TSWV)
 Symptoms:
Cucurbits infected with tospovirus exhibit a variety of symptoms.
Leaves can show bronzing to severe systemic chlorotic spotting.
Other symptoms include leaf deformation, mosaic, die-back and
overall plant stunting.
Fruit symptoms can range from chlorotic ring spots on young fruit
to necrotic lesions on older fruit.
Fruit cracking may also be observe

17. Etiology:
Tospo virus spp. possess a tripartite single-stranded RNA genome with
a negative or ambisense expression strategy.
Genomic RNAs are encapsidated by nucleocapsid proteins (N) and
enveloped by a lipoprotein membrane
Transmission:
Western flower thrips (Frankliniella occidentalis), Tobacco thrips (F. fusca),
Melon thrips (Thrips palmi).
Management
In protected culture and transplant nurseries, utilize mesh screening
(minimum 72 mesh /192 microns) and phytosanitary measures to minimize
tospovirus infection by excluding thrips.
Avoid planting near or downwind of ornamentals or older crops, which
can serve as reservoirs for thrips and tospovirus.
 Control weeds and cucurbit volunteers.
Implement a comprehensive insecticide program beginning prior to
sowing or transplanting to manage thrips early larval stages and limit
secondary tospovirus spread.